Modern computer-controlled telephone communication systems provide a multitude of new possibilities in the use of the telephone. Included among these, for example, is the deferred communication of voice messages that can be deposited in a defined memory area of a central memory arrangement that is permanently assigned to a subscriber. The voice storing and the managed communication of the individual information can be realized both in a public telephone network as well as in private branch exchange systems. A subscriber to whom a memory area of a central memory arrangement is allocated can call in the voice messages deposited for him at a time he can freely select. In addition to recording the individual messages by a sender and the call-in by the authorized receiver, it is possible to edit the messages. Thus, for example, the sender can alter or erase the message when inputting the messages into the predetermined memory area of the central memory arrangement. The receiver likewise has various possibilities available to him regarding the messages deposited for him. Thus, he can call messages deposited for him in different parts or a number of times, can select specific messages, can combine them with his own message and can erase the originally deposited message at a freely selectable time. For user prompting in dialogue between a user of the system and the system, optical information displayable on terminal equipment, instructions in spoken form (referred to as prompts) and alerting tones can be provided.
For example, such a communication system is disclosed by German Published Application DE 35 07 343 and by U.S. Pat. No. 4,585,906. The communication system disclosed by the latter patent has a tone generator ("1152", column 42, lines 43-61, FIG. 25b) that serves the purpose of generating alerting tones, referred to as DTMF (dual tone multi-frequency) sound signals that are each composed of two frequencies.
German Published Application 31 34 328 discloses a method for operating a PCM system as well as for operating of a memory that stores PCM signals. Special digits are provided, that represent arbitrary information such as, for example, markings, that can be input by a terminal user and which can be routed to a user as needed by themselves.